Scott Kelly was a kid with ADHD and bleak prospects. Then he read a book, now he's a record-setting astronaut!

Scott Kelly was never going to win a vote for most likely to succeed. "I was a terrible student," he writes, "always staring out windows or looking at the clock, waiting for class to be over." He and his twin brother were "like juvenile delinquents who never got arrested." His dad was alcoholic. His parents fought, often and violently.

Today, he is a veteran of four spaceflights and the man who holds the record for longest single space mission by an American.

When you look back at your youth, do you think you succeeded despite the obstacles, or perhaps because of them?

In some ways it was — what's the saying? "What doesn't kill you makes you stronger." And you can learn lessons from people's bad traits as well as the good. I think in some ways living with conflict made my brother and me good at dealing with conflict. And that can be helpful in life.

The ADHD thing was a challenge because I was trying to get an engineering degree and learn technical stuff, which wasn't necessarily easy for me. But at the same time, I've often found that one of the things that I was good at in space was prioritizing and focusing on the stuff that was really, really important. And it was easy for me to ignore the less important stuff — to say, "I don't care about that."

I've noticed other astronauts in space for long periods of time that are very ultra-Type A overachievers who have to do everything perfect — struggle with letting things go and not being able to do everything exactly perfectly. It was easy for me to ignore stuff that didn't matter as much.